The disclosure of Japanese Patent Application No. HEI 10-219471 filed on Aug. 3, 1998 and HEI 11-1423332 filed on May 21, 1999 including the specification, drawings and abstract is incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a method of manufacturing a multiple uneven plate having an overall plate shape, provided with multiple uneven portions by forming a plurality of concave or convex portions on at least one surface of the plate, and further relates to the multiple uneven plate and a fuel cell separator using the multiple uneven plate.
2. Description of the Related Art
Materials having an overall plate shape and provided with multiple protrusions (convex portions) on one or both of the surfaces thereof as well as depressed portions (concave portions) formed following the formation of the protrusions, i.e., multiple uneven plates, have been put to practical use in various fields. Multiple uneven plates of this type have various purposes or functions. It is possible to increase strength by, for instance, providing a plurality of convex portions and concave portions on, for example, a plate member and by thereby increasing a geometric moment of inertia. Also, convex and concave portions are provided for the purpose of increasing the entire surface area of a plate member. Furthermore, convex portions may function as contact points with other members or supports therefor.
In any case, it is necessary to provide the convex and concave portions integrally with the flat plate member which serves as a base member. For that reason, multiple uneven plate manufacturing methods are based on deformation of a plate member (such as a metal plate) in a direction of a thickness of the plate by pressing. In addition, if different functions are required for the convex portions and the flat plate member (base member), they may be made of different materials. In that case, therefore, axial or pin-like members which become convex portions, are joined to the flat plate member while the members are kept in a vertical state. As a method of manufacturing a multiple uneven plate having convex portions and a plate member made of a different material, there is proposed, for example, a method of joining members for convex portions to the flat plate member by welding or bonding. There is also proposed a method of integrating convex portions with a base member by inserting members for convex portions into holes formed in a flat plate member and then squelching the convex members (by so-called caulking).
Manufacturing the above-stated multiple uneven plate by partially deforming a metal plate to form a plurality of convex and concave portions, may cause the material to be elongated or fluidized. Even with metallic materials having excellent ductility, elongation and fluidization are limited. Due to this, in many cases, the height of a convex portion to be formed or the depth of a concave portion is limited to about 1.5 times the thickness of the material, with the result that necessary uneven shapes cannot be manufactured. To solve this problem, there is proposed a method of repeated ironing of the material. With this method, however, the number of working steps increases and productivity deteriorates. Besides, the application of this method is disadvantageously limited to a case where material can be sufficiently supplied to the convex and concave portions to be formed.
Moreover, when manufacturing a multiple uneven plate having multiple convex and concave portions formed adjacent to one another, the quantity of material used to form the convex and concave portions is limited. Thus, the height of the convex portions and the depth of the concave portions is limited, as well. Normally, the ratio of diameter and pitch of uneven (convex and concave) portions must be set at 2.5 or more. In this respect, the shape of the multiple uneven plate is disadvantageously limited.
In contrast, if the method of manufacturing a multiple uneven plate by joining a plurality of members for convex portions to a flat plate member is adopted, the material is not deformed and, therefore, there is no limit to the shape. However, if members are joined by means of welding, the material is molten. Due to this, if convex portions are as small, e.g. several millimeters in diameter, and the pitches. thereof are narrow, it is quite likely that the members for the convex portions will be molten and lost. If an adhesive agent is used, by contrast, it is not only difficult to ensure conductivity between the convex portions and the flat plate member, it is also difficult to ensure sufficient joint strength and durability.
If the convex portions are joined to the flat plate member by means of caulking instead of the above two means, it is required to form holes through which the convex members are inserted into the flat plate member. This disadvantageously increases the number of working steps. Besides, the inner diameter of a hole should be larger than an outer diameter of a convex member so as to facilitate insertion of the convex member into the hole. The clearance between the hole and the convex member should then be tightly sealed by caulking the convex member. With caulking, it is possible to form the convex members integrally with the plate member; however, it is difficult to ensure an airtight seal. For these reasons, it is difficult to adopt caulking to the manufacture of various multiple uneven plates.
As stated above, the-manufacture of a multiple uneven plate has disadvantages in that working limitations hamper increases in the heights of convex portions and the depths of concave portions or must widen their intervals and limit the shape of the multiple uneven plates. Furthermore, to solve these disadvantages, other disadvantages, such as the number of working steps may increase, reliability may deteriorate, product cost may increase and quality may deteriorate.
Under these circumstances, the present invention has been made. It is, therefore, an object of the present invention to provide a method of manufacturing a multiple uneven plate and a fuel cell separator using the multiple uneven plate which dispense with limitations of shapes of convex and concave portions and pitches and which have high productivity.
To obtain the above object, the present invention in a first embodiment is a method of manufacturing a multiple uneven plate having a plurality of mutually independent uneven portions formed on front and back surfaces thereof, the method comprising the step of forming a plurality of grooves on at least one surface of a plate member, a thickness of the plate member at each of the grooves being reduced relative to a thickness of the plate member outside the grooves and bending the plate member to form a plurality of trough lines and crest lines, the trough and crest lines being oriented to cross the grooves.
With this method, it is possible to reduce xe2x80x9celongation degreexe2x80x9d and xe2x80x9cstretching degreexe2x80x9d of the material and to form a plurality of mutually independent uneven portions mainly by bending. Thus, it is possible to manufacture a multiple uneven plate including uneven portions each having a large height or depth and adjacent to one another.
The present invention in a second embodiment is a method of manufacturing a multiple uneven plate to include a plurality of concave portions formed on one surface thereof, the method comprising the steps of placing the plate member on a die and vibrating and pressing a punch against one surface of the plate member in at least one of a thickness direction of the plate member and a plane direction of the plate member.
With this method, while the elongation of material occurs to part of the uneven portions, the overall uneven portions are gradually finished into a predetermined shape. Thus, creeps hardly occur. As a result, it is possible to form uneven portions each having a depth larger than the plate thickness.
The present invention in a third embodiment is a method of manufacturing a multiple uneven plate having a plurality of convex portions provided on one surface thereof, the method comprising the steps of placing the plate member on a die and pressing a plurality of axial members against at least one surface of the plate member and pressurizing each of the axial members in axial direction thereof and fitting each of the axial members into the plate member to thereby integrate the axial members with the plate member.
With this method, the punches serve as the axial members which are protruding members and the axial members are fitted and integrated into the plate member. Thus, it is possible to easily manufacture the multiple uneven plate. In addition, the material for the plate member is not fluidized or elongated. It is, therefore, possible to put the respective protrusions close to one another and to lengthen the protrusions. As a result, it is possible to obtain a multiple uneven plate having many protrusions per unit area and having protruding degrees. It is also possible to change the material of the plate member and that of the protrusions (axial members), if necessary.
The present invention in a fourth embodiment is a method of manufacturing a multiple uneven plate including a plurality of concave portions depressed from one surface of a plate member toward the other surface of the plate member, the method comprising the steps of causing deformations accompanied by fluidization of the plate member to one portion of the plate member, to be provided with the concave portions, for each of a plurality of regions divided to include a plurality of concave portions, to thereby form the concave portions.
With this method, while the concave portions are formed by causing material fluidization in the plate member, the working is executed in one portion of divisions determined in advance. Due to this, material is not introduced from the same portions at a plurality of worked portions. This makes it possible to advance the formation limit and to form concave portions or convex portions each having a larger depth than the plate thickness. Besides, the working is executed simultaneously in a plurality of divisions, so that there is not fear of the deterioration of productivity.
The present invention in a fifth embodiment is a fuel cell separator comprising a multiple uneven plate, the multiple uneven plate having a plurality of first grooves formed in a first surface thereof, a thickness of the plate being smaller in each first groove than a thickness of the plate outside the first grooves, the plate being bent to form a plurality of second grooves, the second grooves forming a corresponding plurality of trough and crest lines, the trough and crest lines crossing the first grooves. With this structure, the convex portions determined by the first and second grooves become contact points electrically continuous to the electrodes of the fuel cell, and these grooves can be used as channels for gas and coolant.
According to this embodiment, the grooves formed on the first surface form cooling water channels and the grooves formed on the second surface form gas channels. Due to this, it is possible to form gas channels and cooling water channels using a single separator or a pair of separators.
Preferably, upstream side first grooves in a flow direction of cooling water may differ from downstream side first grooves in array or shape. By doing so, the flow rate of cooling water distributed into the second grooves through the first channels can be controlled by the shape or array of the first grooves. Also, it is possible to sufficiently secure the quantity of cooling water for each of the second grooves to thereby prevent occurrence of cooling defect.
Moreover, the separator may include a plurality of third grooves formed on the second surface thereof by bending the plate in portions corresponding to crest lines on the first surface of the plate member to cross the crest lines, wherein the first grooves and second grooves on the first surface form cooling water channels, and the second grooves and the third grooves on the second surface form gas channels. By doing so, it is possible to use one of the surfaces of the plate member as a cooling part through which cooling water flows and the other surface thereof as a gas supply and discharge part for gas supplied for powering the fuel cell. Besides, the grooves are formed to cross one another on each of the surfaces. This makes it possible to accelerate the distribution of cooling water and gas.
In addition to the above constitution, it is possible to form fourth grooves having a larger cross sectional area than a cross sectional area of the third grooves, the fourth grooves being formed on the second surface of the plate by pressure-deforming predetermined portions of the plate corresponding to crest lines on the second surfaces of the plate member in a plate thickness direction.
By so forming, the fourth groove having a larger cross-sectional area than that of the third grooves are formed as grooves for communicating with the second grooves formed by bending in the gas supply part on the second surface of the plate member. Due to this, it is possible to introduce liquid such as droplet in the gas channels into the fourth grooves, or to distribute the liquid to other second grooves through the fourth grooves. As a result, it is possible to get rid of the clogging of the second grooves due to droplet and to realize good gas flow and distribution.
The present invention in sixth embodiment is a method of manufacturing a separator, the method comprising the steps of forming a plurality of first parallel grooves on a plate member by first work method and forming a plurality of second parallel grooves being oriented to cross the first grooves on the plate member by second method different from the first work method.